definition/meaning

what is really meant by this......

SatNW winds 5 to 15 kt. Wind waves 1 to 3 ft. NW swell 2 to 3 ft at 8 seconds. Patchy fog in the morning. Slight chance of thunderstorms in the morning.

Sat NightNW winds 5 to 15 kt. Wind waves 1 to 3 ft. NW swell 2 to 3 ft at 8 seconds. Slight chance of thunderstorms after midnight.
SunNW winds 10 kt. Wind waves 2 ft or less. NW swell 2 to 3 ft at 9 seconds. Slight chance of thunderstorms in the morning.

what is meant by slight chance? 2%, 5%, 10%, 20%? why can't it just say 15% chance or something like that?
This shouldn't concern much getting out on the water right?

you can check a local weather forecast for more information on what comes from the sky...

I forgot what rain looks like.  Been so long.

I'm looking at another source and it says 0% chance precipitation. for Monday there is a 10% chance.